The build-up of petroleum residue, such as asphalt and asphalt-related liquid, on processing equipment used in highway and road construction, as well as on equipment used in petroleum and chemical processing, storage and transport, has long been problematic. After a certain level of buildup occurs, the equipment is often no longer capable of being used for its intended purpose. Accordingly, it becomes necessary to clean such equipment. Diesel fuel (or a similar type of fuel) has been used in the past for cleaning construction equipment. The use of diesel fuel-based solvents, however, has largely fallen into disfavor due to heightened environmental concerns. See, e.g., Federal Water Pollution Control Act Amendments of 1972, Pub. L. 92-500, §311(b)(1).
Several biodegradable solvents have been formulated as an alternative to diesel-fuel for removing petroleum residue from a substrate. Most of these solvent compositions, however, do not meet all of the requirements mandated by the United States Department of Transportation (U.S. DOT) for a solvent to be considered as an environmentally benign biodegradable substitute for diesel fuel. The main criteria set forth by the U.S. DOT (through the adoption of the U.S. Environmental Protection Agency (EPA) regulations) for a solvent composition to be accepted as an efficient, environmentally friendly substitute for diesel fuel are given as follows:
First, the solvent should be biodegradable and pose no health hazards. There is no single definition of biodegradability, however, throughout the United States and internationally there is a wide range of environmentally preferable definitions. The ASTM standards committee has defined biodegradability in terms of the degree of degradation, time, and test methodology. Despite these definitions, there are two widely used designations for biodegradability: readily and inherently. Readily biodegradable is defined as degrading 80 percent within 21 days as measured by the decrease of a test sample. This type of degradation is preferable because, in most cases, the fluid will degrade long before environmental damage has occurred. Thus, readily biodegradable materials require little in terms of long-term bio-remediation. Inherent biodegradability, is defined as having the propensity to biodegrade, with no indication of timing or degree.
Second is efficiency. A solvent could be biodegradable, but still be inefficient in removing the binder from the surface of a substrate, e.g., asphalt paving equipment. Therefore, a successful substitute for diesel fuel should have the ability to remove asphalt residue buildup with an efficiency value that is equal to, or greater than, that of diesel fuel. In this respect, the North Carolina Department of Transportation (NCDOT), in collaboration with the Department of Civil Engineering, North Carolina State University, Raleigh, N.C., devised a standard method for assessing the efficiency of diesel fuel biodegradable solvent substitutes. See Kulkarni, M., et al., J. of Testing and Evaluation, 31(5), 429-437 (2003). According to this method, a solvent that has an efficiency value that is equal to or greater than that of diesel fuel in removing asphalt binder coated on an aluminum surface is considered acceptable as a successful substitute for diesel fuel, provided that it meets all other environmental, health, and fire hazards criteria.
The standard method can be briefly described in the following steps: Contacting a specified mass of asphalt binder (e.g., bitumen) having a specified surface area with a specified mass of the solvent for a specified period of time, followed by a water rinsing step for a specified period of time, drying to constant weight in an oven, and finally calculating the weight loss of the asphalt layer as a percentage efficiency of the solvent (the greater the amount of asphalt removed, the higher the efficiency value). For every solvent tested, a control sample of diesel fuel is tested for comparison, and the solvent that scores an efficiency value equal to or greater than that of diesel is accepted as an efficient environmentally benign substitute for diesel fuel. The reason for implementing the water rinse step is to simulate the fact that asphalt paving workers usually apply the cleaning solvent on their equipment or truck beds, followed by water rinsing to prevent the residual cleaning solvent from stripping bitumen (often referred to as “binder” in the asphalt industry) from the asphalt. Typical binder contents in most asphalt mix designs range from 3 to 8 wt %. Stripping of the binder by the solvent is undesirable because this will result in decreasing the amount of binder in the asphalt mix, which will downgrade the asphalt quality and render it out of specification. Stripped asphalt mixes are more vulnerable to fatigue cracking and the presence of the solvent in the mix will alter the viscosity of the mix by making it softer than designed, which will alter the mechanical properties of the asphalt. On the other hand, the presence of the residual asphalt cleaning solvent will not allow the proper application of an asphalt release agent, which is needed to prevent the asphalt from sticking to the equipment surface, or truck bed. Therefore, based on these factors, it is desirable, from the application point of view, that the solvent be water compatible/soluble.
Third, the solvent should not pose fire hazards during application, and/or storage. In this respect, the U.S. DOT Hazardous Materials regulations define flammable liquids as having a flash point of less than 141° F. (60.55° C.). See U.S. Department of Transportation Hazardous Materials Regulations, 49 C.F.R. Part 173.120. Another closely related definition is found in the U.S. EPA Hazardous Waste regulations. See U.S. Environmental Protection Agency Regulations, 40 C.F.R. Part 261.21. The EPA regulations define an ignitable liquid as having a flash point less than 140° F. (60° C.). Both sets of regulations require the flash point to be determined by a closed-cup ASTM D-93 method. Although pure d-limonene is considered to be an environmentally benign, efficient asphalt solvent, its low flash point (46° C.) prevents it from being used solely as a substitute for diesel fuel. Any solvent formulation that contains d-limonene in a percentage low enough not to bring the flash point of the formulation below 60° C., however, probably would be considered an acceptable non-ignitable solvent.
Fourth, the solvent should not contain trace amounts of Volatile Organic compounds (VOCs) above the limit mentioned in EPA method 8260B, Office of Solid Waste, United States Environmental Protection Agency, incorporated herein by reference in its entirety. This standard method describes the use of a Gas Chromatography-Mass Spectroscopy (GC-MS) method of analysis to detect VOCs in different substrates, such as ground and surface water, aqueous sludges, caustic liquors, acid liquors, waste solvents, oily wastes, mousses, tars, fibrous wastes, polymeric emulsions, filter cakes, spent carbons, spent catalysts, soils, sediment soil, and water streams.
Fifth, the solvent should have a neutral pH value, i.e., a pH value of about 7, and not have a corrosive effect on the metal surfaces and containers.
Due to the lack of a solvent formulations that would comply with all five primary criteria required for an environmentally benign asphalt solvent, the presently disclosed subject matter was developed to fill the need for improved solvent compositions and methods for removing petroleum residue, in general, and bitumen, in particular, from a substrate.